The European Aerosol Research Lidar Network (EARLINET) is the first continental-scale lidar network for vertical aerosol profiling. The major activities and results are highlighted

This paper will explore the possibility of using vertical profiles of temperature and relative humidity retrieved by a surface-based multifrequency microwave profiling radiometer to determine the bases and tops of clouds as well as amounts (sky cover) of individual layers using a technique originally developed by Chernykh and Eskridge (CE) for radiosonde profiles. The CE method determines the presence of cloud layers by monitoring the second derivative of temperature T(z) and relative humidity R(z) vertical profiles. Necessary conditions for detection of cloud layers are: T"(z) >= 0 and R"(z) <= 0. We have improved this algorithm by using supplementary retrieved data not measured by radiosondes: the cloud base height estimated by an infrared thermometer and the liquid water path L. This extra set of conditions can be summarized as follows: a cloud contains liquid water whenever the retrieved L exceeds a certain threshold value and its cloud base height is lower than some maximum value. The cloud amount is estimated using the minimum dewpoint depression within the detected layer and the corresponding temperature. This dependence of cloud amount on dewpoint depression and temperature is presented in the form of a new Arabey diagram empirically derived for the liquid water and mixed-phase cloud climatology of the Ottawa area. Comparisons will be made between predictions based on this improved cloud detection algorithm for low and midlevel clouds as well as cases of clear skies and co-located "ground truth" surface observations using daytime data collected in Ottawa between the fall of 2004 and the summer of 2005. These sky observations are based on WMO Cloud Atlas descriptions supplemented by hourly surface observations of cloud cover from the Ottawa Airport. Our new algorithm has been shown to significantly reduce the number of false positives.

Clouds play a crucial role in the climate system. The investigation of their radiative properties on the cloud optical, microphysical, and geometrical characteristics is of great interest. Here, top height, base height, and geometrical thickness of cloud layer are considered as cloud geometrical properties. Several studies show that information of some spectral regions including oxygen A-band, enables us to retrieve the cloud geometrical properties as well as the optical thickness and the effective particle radius of cloud. In this study, an algorithm was developed to retrieve simultaneously the cloud optical thickness, effective particle radius, top height, and geometrical thickness of cloud layer with the spectral information of visible, near infrared, thermal infrared, and oxygen A-band channels. This algorithm was applied to ADEOS-II / GLI. For the preparation of global analysis, we look into the look up tables for the sensitivity of cloud optical thickness, particle size, top height, and geometrical thickness. This study will expand to the global analysis and is anticipated to contribute to the earth climate studies in terms of cloud optical, microphysical, and geometrical properties.

The Infrared Atmospheric Sounding Interferometer (IASI) , due to fly on the EPS Metop satellites from 2006 onwards, will produce hyperspectral radiance spectra, profiles of temperature and humidity at high vertical resolution in addition to columnar trace gas amounts, skin temperature, surface emissivity, and cloud products. Since IASI is not an ideal interferometer, any inhomogeneity within the instrument's field of view (FOV) changes the self-apodisation and thus modifies the spectral response. Clouds and surface variability are likely sources of such inhomogeneities that need to be known in order to correct for the changed spectral response and perform the atmospheric retrievals to the specified accuracy. The operationally generated AVHRR (Advanced Very High Resolution Radiometer) scenes analysis is used to identify the surface or cloud types present in each IASI FOV. However, although statistically averaging the scenes analysis results to obtain mean estimates of cloud coverage and scene type within the IASI pixels increases the probability of correct classification, the geometric distribution of each scene is lost. A radiance analysis is performed on the co-located AVHRR pixels to identify localised areas of similar radiance clusters within the IASI pixels, the assumption being these clusters correspond to different scene types. Similar clusters of known scene type are then generated from the AVHRR scenes analysis data and matched to the clusters generated from the independent radiance analysis in order to classify scenes in IASI fields of view.

Geostationary satellites are well suited for radiation budget computations due to their high temporal resolution. In order to validate satellite observations and the radiative properties derived from the GMS-5/SVISSR, we compared its cloud optical depth (COD) with that from the polar orbiting satellite, TERRA/MODIS. It appears that there's a good agreement between both COD sets in thin cloud areas while, major differences (MODIS COD higher) occur in thick cloud regions. Factors affecting accurate observations of clouds by satellites range from the solar and satellites geometries to the sun-cloud scale of interaction. This study focuses on the latter effect, as the solar and satellite zenith angles are relatively low in the area and time selected. The sun-cloud interactions refer here to the three-dimensional radiative effects (e.g. asymmetry, smoothing) due to the horizontal spatial variability of clouds and their structural inhomogeneity. These are analyzed through the IR thermal gradient and small areas' standard deviation (STDEV) respectively. By combining these two parameters, it is possible to reasonably explain the differences in cloud physical and optical properties noticed between both satellites. Results show that, asymmetry and smoothing effects seem to be stronger for SVISSR data than MODIS. At the sides of the clouds SVISSR observed cloud properties are more or less comparable to MODIS data. At the top of the clouds, SVISSR data are systematically lower and do not match MODIS data. SVISSR observations fail to detect cloud inhomogeneity mostly at the top of the clouds, and therefore seem to underestimate the cloud optical properties.

We developed a low-power and high-sensitivity cloud profiling radar transmitting frequency modulated continuous wave (FM-CW) at 95 GHz for ground-based observations. Millimeter wave at 95 GHz is used to realize much higher sensitivity than lower frequencies to small cloud particles. An FM-CW type radar realizes similar sensitivity with much smaller output power to a pulse type radar. Two 1m-diameter parabolic antennas separated by 1.4m each other are used for transmitting and receiving the wave. The direction of the antennas is fixed at the zenith. The radar is designed to observe clouds between 0.3 and 20 km in height with a resolution of 15 m. Using the developed millimeter-wave FM-CW radar at 95 GHz, we observed clouds in a campaign observation in Amami Island in March 2003, and on a sail on Mirai, a Japanese scientific research vessel, in September 2004 to January 2005 in the Arctic Ocean and the southwest of the Pacific Ocean. The radar provided good and sensitive data in these long-term observations.

We describe joint U.S.-Russian Federation (RF) measurements of cloud scattering and polarization using the cloud chamber at Obninsk and field observations at Gorno-Altaysk. Cloud chamber experiments measure polarized scattering patterns of narrow distributions of ice crystals. These experiments may be supplemented with extended-range, intensity-only measurements. The U.S. team uses its scattering codes to verify intensity measurements involving oriented ice crystals, compares the orientation distributions with theory, and may field sensors to measure the total optical depth and the forward scattering properties of the particles in the cloud layer. Ice clouds present two serious impediments to electro-optical observation systems: clutter in short and mid-wave IR bands, and propagation loss when attempting to see through clouds. In high-altitude clouds, ice particles' mirror-like crystalline structure can produce intense "glint" features viewed from satellite sensors. Polarization can mitigate cloud clutter, since cloud-scattered sunlight is generally polarized, whereas point-source target signals are not. The effectiveness of polarization as a mitigant can in principle be modeled, but the models require validation, which must be based on carefully designed laboratory and field experiments.

Four techniques for detecting multilayered clouds and retrieving the cloud properties using satellite data are explored to help address the need for better quantification of cloud vertical structure. A new technique was developed using multispectral imager data with secondary imager products (infrared brightness temperature differences, BTD). The other methods examined here use atmospheric sounding data (CO₂-slicing, CO2), BTD, or microwave data. The CO2 and BTD methods are limited to optically thin cirrus over low clouds, while the MWR methods are limited to ocean areas only. This paper explores the use of the BTD and CO2 methods as applied to Moderate Resolution Imaging Spectroradiometer (MODIS) and Advanced Microwave Scanning Radiometer EOS (AMSR-E) data taken from the Aqua satellite over ocean surfaces. Cloud properties derived from MODIS data for the Clouds and the Earth's Radiant Energy System (CERES) Project are used to classify cloud phase and optical properties. The preliminary results focus on a MODIS image taken off the Uruguayan coast. The combined MW visible infrared (MVI) method is assumed to be the reference for detecting multilayered ice-over-water clouds. The BTD and CO2 techniques accurately match the MVI classifications in only 51 and 41% of the cases, respectively. Much additional study is need to determine the uncertainties in the MVI method and to analyze many more overlapped cloud scenes.

Trade wind cumulus clouds typically have horizontal sizes of tens of meters to tens of kilometers. Cloud products from MISR and MODIS instruments are available at spatial resolutions varying from 1 km to 5 km. Therefore some of these clouds have been poorly detected and studied. For the duration of the Rain in Cumulus over the Ocean (RICO) experiment, November 2004 - January 2005, data from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is available at 15 meters spatial resolution. We use this data along with a suite of aircraft data available as part of RICO to validate cloud macro-physical properties derived from meteorological satellites.

The Multi-angle Imaging SpectroRadiometer (MISR) currently provides three independently derived cloud mask products at 1.1 km spatial resolution. The Radiometric Camera-by-camera Cloud Mask (RCCM) is terrain-referenced and calculated for each of the nine MISR cameras, the Stereoscopically Derived Cloud Mask (SDCM) is feature-projected and uses radiances from one pair of the MISR cameras, and the Angular Signature Cloud Mask (ASCM) uses a band-differenced angular signature based on the two most oblique cameras viewing forward scattering radiation. While each mask has been extensively validated, each having its own strengths and weaknesses, there has been no effort to combine the strengths of all of the masks to create a single consensus product. We present an algorithm which addresses the problem and produces a so called "consensus cloud mask" of improved performance, and elaborate on further cloud climatology applications.

Cloud altitude measurements by a 532nm backscatter Lidar and time lapsed digital photography are combined to monitor the cloud velocity profile. The cloud images are recorded in time steps of two seconds by a Nikon D100 digital camera through a 63° solid angle while the Lidar was measuring the cloud altitude. The images are recorded in 8 bits gray scale JPG format in an array of 2240×1488 pixels. To measure the angular displacement of different parts of the cloud, each image is meshed into an array of 44×29 cells, each cell contains 50×50 pixels. The grayscale density cross correlations between similar cells of successive images are computed using a MATLAB code developed by us for this application. The output products are the direction and the amount of displacement of each cell, in pixels. combining the results on cloud displacement with Lidar measurements enable to calculate the velocity vector in each cell. The resolution in velocity is about 1 ms^-1 and 2° in direction. The calculation technique also is tested by simulating the cloud motion by moving the image pixels with a computer generated Gaussian velocity distribution.

This paper describes a three-dimensional approach of microwave brightness temperature calculation of rain field using TRMM PR data. Calculations were made for the Stoke parameters by means of a vector discrete ordinate method toward twenty four directions in a three dimensional space. The results were compared to the TRMM TMI data to evaluate the validity of calculation. Introduction of wind-roughed sea surface model improved the correlation between the calculated and measured brightness temperatures.

Atmospheric Correction Algorithms (ACAs) are used in applications of remotely sensed Hyperspectral and Multispectral Imagery (HSI/MSI) to correct for atmospheric effects on measurements acquired by air and space-borne systems. The Fast Line-of-sight Atmospheric Analysis of Spectral Hypercubes (FLAASH) algorithm is a forward-model based ACA created for HSI and MSI instruments which operate in the visible through shortwave infrared (Vis-SWIR) spectral regime. Designed as a general-purpose, physics-based code for inverting at-sensor radiance measurements into surface reflectance, FLAASH provides a collection of spectral analysis and atmospheric retrieval methods including: a per-pixel vertical water vapor column estimate, determination of aerosol optical depth, estimation of scattering for compensation of adjacency effects, detection/characterization of clouds, and smoothing of spectral structure resulting from an imperfect atmospheric correction. To further improve the accuracy of the atmospheric correction process, FLAASH will also detect and compensate for sensor-introduced artifacts such as optical smile and wavelength mis-calibration. FLAASH relies on the MODTRAN^TM radiative transfer (RT) code as the physical basis behind its mathematical formulation, and has been developed in parallel with upgrades to MODTRAN in order to take advantage of the latest improvements in speed and accuracy. For example, the rapid, high fidelity multiple scattering (MS) option available in MODTRAN4 can greatly improve the accuracy of atmospheric retrievals over the 2-stream approximation. In this paper, advanced features available in FLAASH are described, including the principles and methods used to derive atmospheric parameters from HSI and MSI data. Results are presented from processing of Hyperion, AVIRIS, and LANDSAT data.

The peculiarities of the light fields forming in the clouds are their complicated geometrical three-dimensional shape and strongly anisotropic light scattering. In these conditions the solution of the radiative transfer equation becomes mathematically ill-conditioned. The problem has a fundamental character and is concerned with a physical model of the radiation transfer-ray approximation, which determines the presence of the angular singularities in the solution. For the elimination of this problem S.Chandrasekhar has offered to subtract nonscattered radiation from the solution and to state the equations for the rest smooth part. However in the conditions of the strong anisotropic scattering the similar approach loses its efficiency. The most optimal approach in the solution of this problem is the determination of the analytically simple approximate solution including all the angular singularities of the exact solution. An example of such an approach is a small-angle approximation in the Goudsmit-Saunderson form, which however is obtained only for the flat medium geometry at an almost normal incident of the solar radiation.

The Spinning Enhanced Visible and Infrared Imagery (SEVIRI) instrument, on board the Meteosat Second Generation (MSG), is a radiometer with eight infrared (IR) spectral bands. Layer Precipitable Water (LPW) from MSG SEVIRI, over the northern hemisphere area covered by MSG (MSG N), has been developed by INM within the EUMETSAT SAFNWC (Satellite Application Facility on support to Nowcasting and Very Short-Range Forecasting) framework. Seven of the SEVIRI IR channels are used to retrieve the LPW (Layer Precipitable Water) using neural networks. The Total Precipitable Water (LPW(TPW)) is one of the LPW parameters. The LPW(TPW) is routinely generated every fifteen minutes at a satellite horizontal resolution of 3 km in nadir on clear air pixels. Total column Integrated Water Vapor data derived from Zenith Total Delay GPS (Global Positioning System) data (GPS_IWV) and surface measurements/NWP estimations, are provided by eleven different ground based GPS data processing centres participating in the TOUGH EU Project in near real time (NRT). A set of LPW(TPW) values co-located with GPS_IWV stations has been added to NRT GPS data that are being routinely introduced in passive mode in the Hirlam 3DVar Assimilation system operational at INM. This paper will show an intercomparison of total column integrated water vapor from the HIRLAM first guess for the 3DVar analysis, the NRT GPS_IWV data and the LPW(TPW) product.

The purpose of this work is to compare top of the atmosphere (TOA) radiances as measured by the Geostationary Earth Radiation Budget (GERB) instrument on board the METEOSAT-8 (METEOSAT Second Generation) satellite to equivalent independent radiances obtained from radiative transfer simulations performed using surface and atmospheric measured parameters gathered during the GERB Surface Ground Validation Campaign at the Valencia Anchor Station (VAS) reference area in February 2004. In this paper we try to extend the methodology previously developed and tested for the NASA Clouds and the Earth's Radiant Energy System (CERES) instrument in the framework of the SEVIRI and GERB Cal/val Area for Large scale field ExperimentS (SCALES) project, to validate GERB much lower spatial resolution data (pixel size of the order of 60 x 60 km² over the VAS). The study also includes the selection of atmospheric profiles from on-purpose radiosonde and GPS (Global Positioning System) data, a BRDF (Bidirectional Reflectance Distribution Function) estimation for the large-scale study area and Streamer radiative transfer simulations of TOA shortwave and longwave radiances.

The Moderate Resolution Imaging Spectroradiometer (MODIS) project has operationally provided land surface temperature (LST) and emissivity imagery produced from mid-infrared bands by either of two atmospheric correction algorithms. One is the generalized split-window algorithm. This algorithm can be applied to each observed scene, and the spatial resolution of generated products is 1 km, but the emissivity data in the products are empirically estimated by a classification-based method. Another is the physics-based day/night algorithm. In this algorithm, both LST and emissivity are physically determined using mid-infrared measurements, but a pair of day/night scenes is necessary for each processing, and the spectral resolution of generated products is degraded to 5 km. In the present paper, the water vapor scaling (WVS) method (Tonooka, 2001 and 2005) is applied to three MODIS thermal infrared (TIR) bands (29, 31, and 32) as an alternative approach. This method is an atmospheric correction algorithm for TIR multi-spectral data including land surfaces, designed mainly for the five TIR spectral bands of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on the Terra satellite. The WVS method is on the basis of a traditional approach using a radiative transfer code, such as MODTRAN, combined with external atmospheric profiles, but the errors included in profiles are reduced on a pixel-by-pixel basis using an extended multi-channel approach. In the present paper, the WVS method for the three MODIS TIR bands is proposed, and applied to actual imagery for preliminary validation.

The paper presents the results of using the MODIS Atmosphere Products satellite information to study the atmospheric characteristics (the aerosol and water vapor) in the Tomsk Region (56-61°N, 75-90°E) in 2001-2004. The satellite data were received from the NASA Goddard Distributed Active Archive Center (DAAC) through the INTERNET.To use satellite data for a solution of scientific and applied problems, it is very important to know their accuracy. Despite the results of validation of the MODIS data have already been available in the literature, we decided to carry out additional investigations for the Tomsk Region. The paper presents the results of validation of the aerosol optical thickness (AOT) and total column precipitable water (TCPW), which are in good agreement with the test data. The statistical analysis revealed some interesting facts. Thus, for example, analyzing the data on the spatial distribution of the average seasonal values of AOT or TCPW for 2001-2003 in the Tomsk Region, we established that instead of the expected spatial homogeneity of these distributions, they have similar spatial structures.

We recently developed a new version of our analysis algorithm for Multi-Filter Rotating Shadowband Radiometer (MFRSR) data that allows us to retrieve fine mode and coarse mode aerosol optical thickness as well as the effective radius of the fine mode. Our retrieval products also include time series of column amounts of ozone and nitrogen dioxide. The algorithm has been tested using a multi-year dataset from the local MFRSR network at the DOE Atmospheric Radiation Measurement (ARM) Program site in Southern Great Plains (SGP). Here we present an overview of the retrieval algorithm and validate its performance through comparison of our MFRSR retrieval products with the corresponding AERONET almucantar retrieval results derived from a CIMEL sunphotometer co-located with the MFRSR at the SGP Central Facility. A constrained variant of the retrieval algorithm (assuming zero nitrogen dioxide column values) is described in detail. We use this variant of the algorithm to derive the range of physically justified values of the fine mode effective radius and for comparison with AERONET particle size retrievals. A multi-instrument, multi-year, MFRSR dataset from the SGP Extended Facilities is used to examine geographical and seasonal variability of aerosol properties. We find a correspondence between the geographical variation in fine mode particle size and aerosol composition (nitrates vs. sulfates) as measured by National Atmospheric Deposition Program. A similar correspondence in terms of temporal variability exists between our retrievals and in-situ measurements of aerosol composition made by NOAA Pacific Marine Environmental Laboratory (PMEL) at SGP Central Facility.

Upper-level divergence is often associated to low-level convergence through the principle of mass continuity, inducing an ascending motion of the air mass. Vertical motion, either upward or downward, is recognized as an important parameter in the atmosphere because it affects the formation or dissipation of clouds. An important application of vertical motion observations is to use this quantity as diagnostic for the occurrence of rain. For instance, extensive regions of precipitation associated with extratropical cyclones are regions of large-scale upward motion. Similarly, the nearly cloud-free regions in large anticyclones are regions in which air is subsiding. Previous studies indicated that the upper tropospheric humidity (UTH) field is also governed by large scale dynamics, and is in a general good agreement with the patterns of high level wind divergence. That suggests that a divergence parameter could be very useful in the analysis for numerical weather prediction. Holmlund (2000a) has described the possibility to infer divergence fields from Atmospheric Motion Vectors (AMVs) that have been derived from tracking cloud and humidity features in the 6.2 μm WV channel of Meteosat. Such algorithm has been developed at EUMETSAT, and tested on Meteosat 8 data. This paper describes the calculation's process of the upper level divergence, and presents some results over large scale convective systems observed by Meteosat 8 over tropical areas.

Ozone profiles retrieved from SAGE III limb scatter measurements are compared with correlative measurements made by two occultation instruments (SAGE II, SAGE III), a limb scatter instrument (OSIRIS) and a series of ozonesondes, in order to ascertain the accuracy and precision of the SAGE III instrument in limb scatter mode. The measurement accuracy is found to be 5-10% from the tropopause to about 45km whereas precision is found to be less than 10% from 20 to 38km. The main source of error is height registration uncertainty, which is found to be Gaussian with a standard deviation of about 400m.

Ground-based sunphotometry measurements can be used to investigate atmospheric aerosol optical properties, such as the volume size distribution, an important parameter in the study of the effect of aerosol on atmospheric processes. Most inversion algorithms assume constant aerosol optical characteristics over the whole air column. In this work we present observational evidence of the limitations of this simplifying assumption in cases where the aerosol vertical structure is highly inhomogeneous. During the field campaign VELETA 2002, carried out in Granada (Spain), a quite complete characterization of the atmospheric aerosol was obtained by simultaneously measuring the columnar aerosol characteristics, by means of CIMEL C318 sun-tracking photometers, the size-segregated near-surface aerosol mass concentration by a GRIMM 1108 dust monitor and the aerosol vertical profiles by a lidar system. During the last days of the campaign, a dust-rich air mass from the Sahara reached the site, producing a multilayered structure on the aerosol vertical profile. The ground level size distributions can be compared with the columnar ones using retrieved scale height values from a lidar extinction coefficient profiles, corresponding to the altitude where the integrated extinction is equal to 1-e^-1 of the AOD. Comparisons of the column-integrated and the modified ground-level aerosol size distributions show a good agreement in the days previous to the arrival of the Saharan intrusion, when the aerosols are homogeneously distributed in a well-mixed boundary layer. But, when the vertical homogeneity is reduced due to elevated layers containing desert dust, the column properties clearly deviates from the surface properties. This indicates the importance of verifying the vertical distribution of aerosol in order to correctly relate column and ground-level optical properties.

The NDSA (Normalized Differential Spectral Absorption) method has been proposed for estimating the total content of water vapor (IWV, Integrated Water Vapor) along a tropospheric propagation path between two Low Earth Orbit (LEO) satellites. This method requires a transmitter onboard the first LEO satellite and a receiver onboard the second one. It is based on the simultaneous measurement of the total attenuation at two relatively close frequencies in the Ku/K bands, and on the estimate of a parameter referred to as 'spectral sensitivity'. This approach is potentially able to emphasize the water vapor contribution, to cancel out all spectrally flat unwanted contributions and to limit the impairments due to tropospheric scintillation. The objective of this paper is to analyze the effects of liquid water presence along the propagation LEO-LEO link on the NDSA approach. Results are based on computer simulation and account for different frequency carriers in the 15-30 GHz range and for any value of liquid water content along the propagation path at 3 km tangent altitude.

A scene dependent sensitivity analysis of top of the atmosphere near infrared radiances and polarized radiances to aerosol optical depth was performed. The analysis was performed for the hemisphere of viewing angles. The analysis includes a comprehensive examination of errors resulting from both the assumed aerosol size distribution and optical properties, as well as radiative transfer model assumptions. Three parameters are introduced. These parameters are the signal, the noise and the signal to noise ratio. The angular structure, as well as the angular averages of these parameters, are examined. It was found that, on the average, the top of the atmosphere signal to noise ratio is roughly three times larger for the radiances than for the polarized radiances. As a result, it was concluded that the majority of the information in the retrieval of optical depth is contained in the intensity measurements. The error analysis was used in the development of a two-channel optimal estimation retrieval of aerosol optical depth which utilizes the intensities only. Noise free and noisy synthetic radiances created from radiative transfer simulations are used to analyze the performance of the retrieval. Biases due to a priori constraints, viewing geometry, and forward model noise are analyzed.

We have used two-dimensional correlation on two-dimensional extinction cross-sections measured by a scanning lidar to determine the velocity structure of the salt-spray aerosols. The lidar scans were collected over a reef at Bellows Beach, on the Northeast side of Oahu, Hawaii. The resulting velocity streamlines suggest that lifting of sea-spray aerosols as high as 200 m occurs in the vicinity of opposing horizontal roll vortices. The velocities vary rapidly over distances of less than 500 m and show a complex pattern which is inadequately represented by conventional anemometer measurements.

Airborne atmospheric measurement of nitrogen dioxide (NO₂) column density was performed using the solar spectroscopic method. The measurement was carried out at different altitudes, from 460 to 700 meters above sea level during a flight in Hong Kong (22.2°N, 114.1°E), the People's Republic of China (PRC). In the territory, the boundary layer height in a sunny day is about 1000 meters. Below the boundary layer, most of the NO₂ exists. The airborne solar spectroscopic measurement gives the NO₂ vertical profile below the boundary layer. In particular, the solar spectroscopic measurement requires a solar tracking system to collect the direct sunlight. However, in an acceptable small percentage of error in tracking the sun position, it is possible to collect the direct sunlight manually. In this paper, to reduce the complexity of the experimental setup, the sunlight is collected by a portable miniature CCD spectrometer. In the retrieval of NO₂ column density, the airborne solar spectrum is normalized to a reference solar spectrum, which is taken at a high altitude (11,230 meters) during another flight in Xinjiang (42.208°N, 83.949°E) province, PRC. The column density retrieval is achieved from the normalized solar spectrum using the differential optical absorption spectroscopy. A ground-based off-axis control experiment is also performed to estimate the error in the slant column density from the airborne measurement.

Spaceborne synthetic aperture radar (SAR) systems are used to measure geo- and biophysical parameters of the Earth's surface, e.g. for agriculture, forestry and land subsidence investigations. Upcoming SAR sensors such as the Japanese Phased Array L-band Synthetic Aperture Radar (PALSAR) onboard the Advanced Land Observing Satellite (ALOS) exemplify a trend towards lower frequencies and higher range chirp bandwidth in order to obtain additional information with higher geometric resolution. However, the use of large bandwidths causes signal degradation within a dispersive medium such as the ionosphere. Under high solar activity conditions at L-band frequencies, ionosphere-induced path delays and Faraday rotation become significant for SAR applications. Due to ionospheric effects, blind use of a generic matched filter causes inaccuracy when correlating the transmitted with the received signal. Maximum correlation occurs where the length of the matched filter, based on a synthetic chirp model of the transmitted signal, is adjusted to correspond to that of the received signal. By searching for the proper adjustment necessary to reach this maximum, the change in length can be estimated and used to derive variations in the total electron content (TEC) and degree of Faraday rotation within the ionosphere from all range lines in a SAR image.

The direction, amplitude, and horizontal and vertical wavelengths are intrinsic attributes of Atmospheric Gravity Waves (AGWs) propagating through the upper atmosphere. The observable airglow modulation has been related to intrinsic amplitude through the 'cancellation factor', the horizontal wavelength from image measurements, the observed directions from image motion fields. The vertical wavelength is traditionally obtained using the wave dispersion relationship from the intrinsic phase speed, which is deduced from the observed phase speed in images and the Doppler correction from measured winds with either Na lidar or meteor radar. Methods of extracting vertical wavelength can also be deduced from measurements of phase shift with altitude through multiple airglows. Tomographic and multiple layer methods have been modeled and data has been analyzed to validate the methods. The multiple layer method enables the measurements to be made from ground-based imagers where winds are note available, or from spacecraft where phase speeds can't be measured.

Na Wind/Temperature lidar offers a method to study the dynamics and thermal structure of the mesosphere and lower thermosphere (MALT) through Doppler methods. The University of Illinois system has been operated at both the USAF Starfire Optical Range in Albuquerque, NM (94, 98-00') and at the USAF AMOS Maui facilities with receiving mirrors that are 3.5 m in diameter. An autonomous receiving system is being developed which will provide unrestricted and continuous operational capabilities. The bi-static operational receivers will be coupled with multiple fibers so that Na (589 nm) returns from the MALT region and Rayleigh (355 nm) returns from the stratosphere and mesosphere can be received simultaneously. The system will be described with attention to increased efficiencies in the receiver.

The Institute of Applied Physics of the University of Berne is active in the filed of remote sensing of middle atmospheric trace gases such as ozone and water vapor by microwave radiometry. From the measured pressure broadened spectral lines it is possible to retrieve the vertical distribution of the observed species. One of the radiometers is operating from an aircraft of the Swiss Air Force. For the spectral analysis it uses a broadband acousto-optical spectrometer with a total bandwidth of 1 GHz with 1725 channels, which allows retrievals of altitude profiles from about the flight height up to 60 km. Unfortunately acousto-optical spectrometers proved to be critical under conditions encountered in an aircraft. For this reason the novel approach of using digital Fast Fourier Transform (FFT) spectrometers with a total bandwidth of 25 MHz and with the option to select either 2048 or 4096 channels and another FFT spectrometer with 16384 channels on 1 GHz bandwidth was chosen. In this paper we present first measurements of atmospheric trace constituents using this novel approach with digital FFT spectrometers. We report on critical instrumental aspects such as system stability and linearity that are of fundamental importance for this application.

Intensity measurements of the two lines of the sodium nightglow, at 589.0 and 589.6 nm, show that their ratio is not constant. It is generally assumed that this ratio is fixed, with a value of I(589.0)/ I(589.6) = 2.0. In measurements made at a variety of sites, most often utilizing the echelle spectrographs at large telescopes, it is demonstrated that the ratio typically varies within the 1.3-1.8 range, with 1.6 being a common value. Because the nightglow emission is relatively strong, individual measurements are quite precise. Both the intensity ratio and the summed intensity fluctuate with a semi- annual oscillation. Laboratory spectra of the ratio show a similar variability of values, and the current hypothesis is that the ratio reflects the [O(³P)]/[O₂] ratio of the environment, in the laboratory or in the mesosphere.

In the Earth's upper atmosphere, collisions between ground state CO₂ molecules and translationally excited O atoms effectively populate the bending (v₂) vibrational modes of CO₂. Subsequent relaxation of the v₂ modes occurs through spontaneous or stimulated emission of 15-μm radiation. Much of this radiation escapes into space, thereby removing ambient kinetic energy from the atmosphere. This cooling mechanism is especially important at altitudes between 75 and 120 km where the O atom density is relatively high and the conditions are optically thin. We have performed laboratory measurements to better characterize the vibrational energy transfer efficiency for this system. Several improvements to the experiment have been made since our preliminary manuscript on this topic. The temperature-jump method is used to form vibrationally excited CO₂, and transient diode laser absorption spectroscopy is used to monitor the vibrational level populations following collisions with atomic oxygen. Using this approach, the room-temperature vibrational relaxation rate coefficient, k_O(v₂), has been measured to be (2.0±0.3)x10^-12 cm³s^-1. This value is slightly higher than previous laboratory measurements, which have clustered in the (1-1.5)x10^-12 cm³s^-1 range, and on the low end of aeronomical estimates of (2-6)x10^-12 cm³s^-1.

In a previous study by Zhang and Shepherd, an empirical model for the daytime (sunlit) O(¹S) green line emission layer was deduced using more than 520,000 emission rate profiles observed by he Wind Imaging Interferometer (WINDII) on the Upper Atmospheric Research Satellite (UARS) during 1991-1997. In the model, the peak emission rates and their altitudes, and the widths of both the F-layer and the E-layer of the emission are given as functions of the solar zenith angle χ and solar irradiance using F10.7 as a proxy. With this model, the daytime emission rate directly related to χ and solar irradiance can be calculated and removed, resulting in the residual emission rates. In this paper, the residual emission rates are presented in both geographic and geomagnetic latitude and local time coordinates grouped by seasons and Kp values. The main results are as follows. (1) The residual emission rates show a midday enhancement at the equator and midday depletions at mid-latitudes in the E-layer. Those variations may be attributed to the diurnal tide. The midday equatorial enhancement also occurs in the F-layer. (2) There is a deep gap in the E-layer at 35°S-65°S at the June solstice, which is wider in the morning than in the afternoon when Kp is low, and vice versa when Kp is high. (3) At latitudes poleward of 50° the daytime O(¹S) aurora is conspicuously displayed in geomagnetic coordinates in both layers even for days with low Kp values, peaking at 60-70° geomagnetic latitudes and in the morning sector or in the afternoon sector or both depending on seasons. The aurora is significantly enhanced when Kp is increased. (4) There is a midday (geomagnetic noon) gap at high latitudes in both layers with a width of 3-4 hours. The gap is deepened when Kp is increased. (5) The integrated volume emission rates have similar features at high latitudes to those seen in the peak volume emission rates.

In a previous paper by Zhang and Shepherd, an empirical model for the peak volume emission rate (V_p) and the integrated volume emission rate of the O(¹D) (630 nm) dayglow was deduced from more than 130,000 daytime emission rate profiles observed by the Wind Imaging Interferometer (WINDII) on the Upper Atmospheric Research Satellite (UARS) during 1991-1995. In the model, the emission rates are given as functions of the solar zenith angle (χ) and solar irradiance using the F10.7 cm flux as a proxy. This paper extends the daytime empirical model into the twilight zone and includes the height of the peak emission rate and the width of the emission layer. For a given day, the O(¹D) emission layer during both daytime and twilight-time is found to be sensitive to the solar zenith angle when solar irradiance is treated as a constant. Positive linear relationships are found between the daytime emission rate and cos^1/eχ at χ < 87° the twilight-time emission rate and cos(χ+0.25)^1.8 at 87° less than or equal to χ less than or equal to 104.5°, and the width of the emission layer and cosχ at χ < 87°. A negative linear relationship is found between the peak emission rate and its height at χ < 104.5°. In the long-term, the emission layer varies according to the solar cycle in that both the emission rate and the height of the emission layer increase with increasing solar irradiance. The empirical model provides the peak volume emission rate and its height, and the integrated emission rate, for both daytime and twilight zones, and the width of the daytime emission layer as functions of the solar zenith angle and solar irradiance using F10.7, E10.7, and Lyman-β as proxies. The profiles of the volume emission rate and global morphology of the red line emission therefore can be constructed using the model. Effects of solar storms, and physical precesses and photochemical reactions other than that due to the direct solar energy deposition in the thermosphere can be derived by comparing to the model.

During summer 2003, large areas of the West Canada (Alberta and British Columbia between 50°N and 60°N and between 105°W and 130°W) have undergone very important forest fires, which were detected by Total Ozone and Mapping Spectrometer (TOMS) and MODerate resolution Imaging Spectroradiometer (MODIS). Many Stratospheric Aerosol and Gas Experiment (SAGE) III measurements obtained during this summer and over this region exhibit enhanced aerosol extinctions in the low stratosphere. SAGE III instrument measures the transmitted light through the earth limb using the solar occultation method. Inversion of transmission measurements allows retrieving vertical profiles of concentration of minor gases and vertical profiles of aerosol extinction coefficient at several wavelengths (from 384 to 1545 nm) in the stratosphere. We have analyzed the aerosol spectral extinctions measured during correlative SAGE III events to observe the impact of these biomass burnings on the properties of stratospheric aerosols. We have inferred the aerosol microphysical properties (effective radius, number density, surface area density) assuming two different compositions corresponding to background (sulphate) and biomass burning aerosols. We have also compared the results to values obtained during unperturbed periods. It is found that a large number of aerosols was injected in the stratosphere but we cannot distinguish between both types of aerosols.

Urban air quality is of great interest from health points of view as well as for future planning and decision making. Mapping of dispersion of air pollution is very complex as it depends upon various factors including weather conditions, urban structural features and their topologies. Urban air pollution is quite dependent on the ventilation condition in traffic corridors which is influenced by the aerodynamic roughness parameters of the ground. Air pollution dispersion with a 3D distribution was mapped by using bio-optical mathematical models and interpolation methods, based on ground local measurements of meteorological parameters and aerosol optical thickness as well as satellite data. While SAR (Synthetic Aperture Radar) images with a time variability are very useful for morphological urban structures extraction, Landsat TM, ETM, SPOT, MODIS images data present a wide applicability for air pollution studies. In this paper, dispersion of urban air pollution in Bucharest town, Romania was mapped through establishing the relationship among optical thickness and ground local data for visible, near infrared and thermal infrared band of the Landsat TM, ETM. Dust particulates concentration and the apparent temperature from satellite data is highly correlated for Landsat TM6 (thermal infrared).A linear regression analysis was performed to establish the relationship between satellite and in-situ monitoring data. Optical thickness of green and red bands and difference of at-satellite temperature of thermal infrared band show statistically significant relationships with, particulate matter, black particles and carbon monoxide respectively. Such analysis is of great importance for urban micro-climate and environmental quality assessment.

An analysis of the results of spaceborne fire detection in the Tomsk Region of Western Siberia allows us to conclude the following. Complex situations often arise in satellite observations in the presence of the atmospheric aerosol or the semitransparent cloudiness when standard algorithms cannot detect automatically small-sized fires from space. In such situations, the problem can be solved successfully by using the atmospheric correction of satellite measurements for the distorting effect of the atmosphere based on atmospheric radiance/scattering models. In this case, a priori information on the optical and meteorological parameters of the atmosphere and on the geometry of observations is used. In the present study, some results of numerical simulation and atmospheric correction for the distorting effect of the atmosphere in the problem of fire detection are given.

The problem of many cities in Europe with the new limit values of PM10 of the Directive 1999/30/EC and the discussion about the implementation of PM2.5 monitoring measurements is leading to discuss also about the spatial distribution of PM concentrations. The general objective of ICAROS NET is the development and demonstration of a networked interactive computational environment that allows the integration and fusion of environmental information from remote sensing observations, ground air quality measurements, and pollution transport models in order to minimize uncertainty in decision-making regarding operational air pollution control and abatement. The method of the platform and some results of the ICAROS NET campaigns were described already in the paper SPIE 5571-38. In the case of Munich it was possible to integrate, besides the PM10 concentration determination, the evaluation of PM2.5 and PM1 concentrations. Because of the weather conditions (clouds) and the general problem of permanent background aerosol in the area of Bavaria it was difficult to find out a good clear satellite reference image for the platform. Therefore, background aerosol (urban, suburban and rural) is added. The growth of the particles with a rising relative humidity is considered in the first layer data fusion module. Finally, PM concentrations of new satellite images and results of the ICAROS NET platform are presented and evaluated.

The Scanning Infrared Gas Imaging System of High Resolution (SIGIS-HR) was used to perform non-intrusive measurements of a Boeing 737 and a diesel powered burned (used as a hot gas producer). During the measurements it was observed that the selection of the optimal measurement positions into the plume, visualised by an infrared image from a real-time infrared camera in which the emission intensity of different field of view (FOV) positions into the plume are plotted in false colours, is possible very precisely. This enhanced considerably the probability of detection of infrared radiation emitted by a hot gas plume (e. g. from an in-service aircraft at the ground) for the objective to determine composition and temperature of the exhausts. Using this improved localization of the optimum measurement position into the hot exhaust plume the temperature and the concentrations of CO and NO were calculated. Additionally, the spatial distribution of gas temperature and concentrations of CO, CO₂ and NO into the exhaust plume were determined.

Air pollutant emission rates of aircrafts are determined with test bed measurements. Regulations exist for CO₂, NO, NO₂, CO concentrations, the content of total unburned hydrocarbons and the smoke number, a measure of soot. These emission indices are listed for each engine in a data base of the International Civil Aviation Organisation (ICAO) for four different Air pollutant emission rates of aircrafts are determined with test bed measurements. Regulations exist for CO2, NO, NO2, CO concentrations, the content of total unburned hydrocarbons and the smoke number, a measure of soot. These emission indices are listed for each engine in a data base of the International Civil Aviation Organisation (ICAO) for four different thrust levels (Idle, approach, cruise and take-off). It is a common procedure to use this data base as a starting point to estimate aircraft emissions at airports and further on to calculate the contribution of airports on local air quality. The comparison of these indices to real in use measurements therefore is a vital task to test the quality of air quality models at airports. Here a method to determine emission indices is used, where concentration measurements of CO₂ together with other pollutants in the aircraft plume are needed. During intensive measurement campaigns at Zurich (ZRH) and Paris Charles De Gaulle (CDG) airports, concentrations of CO₂, NO, NO₂ and CO were measured. The measurement techniques were Fourier-Transform-Infrared (FTIR) spectrometry and Differential Optical Absorption Spectroscopy (DOAS). The big advantage of these methods is that no operations on the airport are influenced during measurement times. Together with detailed observations of taxiway movements, a comparison of emission indices with real in use emissions is possible.

The wide field-of-view radiometers aboard the Earth Radiation Budget Satellite operated for 15 years to provide a high quality radiation budget data set for climate research. Following a solar calibration, the radiometers did not return to Earth viewing position, but stopped short of nadir. Since that time, five years of measurements have been taken. Calibrations have been performed by use of special spacecraft maneuvers so that the measurements are well-calibrated. This paper presents the development of algorithms for retrieving the radiation fluxes at the "top of the atmosphere" taking into account the tilt of the WFOV radiometers from nadir.

The international experiment EAQUATE (European AQUA Thermodynamic Experiment) was held in September 2004 in Italy and in the United Kingdom. The Italian phase, performed in the period 6-10 September 2004, was mainly devoted to assessment and validation of performances of new IR hyperspectral sensors and benefits from data and results of measurements of AQUA and in particular of AIRS. It is also connected with the preparatory actions of MetOp mission with particular attention to calibration and validation of IASI products (as water vapour and temperature profiles), characterization of semitransparent clouds and study of radiative balance, demonstrating the role of ground-based and airborne systems in validation operations. The Italian phase of the campaign was carried out within a cooperation between NASA Langley Research Center, University of Wisconsin, the Istituto di Metodologie per l'Analisi Ambientale (CNR-IMAA), the Mediterranean Agency for Remote Sensing (MARS) and the Universities of Basilicata, Bologna and Napoli. It involved the participation of the Scaled Composites Proteus aircraft (with NAST thermal infrared interferometer and microwave radiometer, the Scanning HIS infrared interferometer, the FIRSC far-IR interferometer), an Earth Observing System-Direct Readout Station and several ground based instruments: four lidar systems, a microwave radiometer, two infrared spectrometers, and a ceilometer. Radiosonde launches for measurements of PTU and wind velocity and direction were also performed as ancillary observations. Four flights were successfully completed with two different AQUA overpasses. The aircraft flew over the Napoli, Potenza and Tito Scalo ground stations several times allowing the collection of coincident aircraft and in- situ observations.

The European AQUA Thermodynamic Experiment was devoted to study atmosphere, ocean and land with high resolution measurements. It consisted of two phases: the first one took place in Italy in the 6-10 September period and the second one in England on 13-22 September. In the framework of the EAQUATE Italian phase, an intensive lidar measurement campaign was performed at CNR-IMAA, sited in Tito Scalo (40°36'N 15°44'E, 760 m a.s.l.). Independent measurements of aerosol extinction and backscatter coefficient at 355nm, and aerosol backscatter coefficient at 532 nm were obtained by means of an elastic\Raman lidar. Another Raman lidar allowed the vertical profiling of the water vapour mixing ratio. Both the lidar systems have high vertical and temporal resolution (15 m - 1 minute), allowing a characterization of the Planetary Boundary Layer as well as of the Free Troposphere also in terms of dynamical behaviour. Ancillary instruments were utilized contemporaneously with lidar measurements. In particular 17 Vaisala radiosondes for PTU measurements were launched during the campaign, 10 of these equipped with RS90 sensors, while 7 utilized RS92 sondes equipped with GSP sensors for wind velocity and direction measurement. Furthermore a 12 channels microwave radiometer providing all around the clock measurements of temperature, relative humidity and water vapour content, was used during the campaign together with a ceilometer for continuous indication of the cloud cover.

A general methodology for evaluating the capabilities of a general lidar system encompassing both backscatter (elastic and Raman lidar) and topographic targets is presented. By introducing a well defined atmospheric reference medium and by individually examining and decomposing the contribution of lidar system parameters including lidar transmitter power, fields of view, receiver noise, atmospheric conditions, and sky background on the signal-to-noise-ratio (SNR), we obtain a simple dimensionless parameterization of the lidar system. Using this parameterization, numerical simulations are carried out to determine achievable lidar performance including operation range, minimum detectable gas concentration etc.

The method of passive remote sensing by Fourier transform spectroscopy allows the retrieval of column densities or concentrations of molecules in gas plumes such as exhaust gas plumes of aircraft or vapor plumes emitted after chemical accidents. State- of-the-art retrieval algorithms require two models: a radiative transfer model and an instrument model, the instrument line shape (ILS). The instrument line shape of real Fourier transform spectrometers (FTS) differs significantly from the instrument line shape of an ideal FTS, in particular if the instrument is optimized for high signal-to-noise ratio, which is achieved by interferometer designs with high optical throughput (etendue). The real instrument line shape may be modeled by convolution of the instrument line shape of the ideal FTS with an inherent instrument line shape describing the deviations. In this work, the inherent instrument line shape is modeled by a function which is dependent on a small number of parameters. In order to determine these parameters automatically, a new method has been developed. Spectra of a well-known gas in a gas cell are measured. The measured spectrum is approximated using a least squares fit with a model that contains the parameters of the instrument line shape. The fitting procedure is performed automatically. The instrument line shape model, the experimental setup of the method for the determination of the instrument line shape, and results of measurements using the instrument line shape are presented. In addition to the analysis of spectra with the ILS determined by the new method, analysis results obtained with an ideal instrument line shape are presented to demonstrate the negative effect of an inaccurate instrument line shape on the retrieved column density.

Monitoring of mixing layer height was performed during different measurement campaigns in urban and sub-urban area (Hanover, Munich, Budapest, Zurich, Garmisch-Partenkirchen) by the Vaisala ceilometer CT25K and LD40. These are eye-safe commercial lidars and designed originally to detect cloud base heights and vertical visibility for aviation safety purposes. The data interpretation method was presented last year in the paper SPIE 5571-29. Software for routine retrieval of mixing layer height from ceilometer data was developed. The comparison with mixing layer height retrievals from a SODAR is continued. In the absence of low clouds and precipitation ceilometers can estimate the mixing layer height fairly well. The instruments partly complement each other. For three dimensional in situ measurements a microlight aircraft equipped with sensors for meteorological parameters and aerosols in different size ranges was used. The microlight, due to its slow horizontal speed, high climb rate and low minimum altitude, serves as very flexible platform for profiling the planetary boundary layer up to about 4500 m a.s.l. on a regional scale. For the measurements of the size distribution of large particles a Grimm aerosol spectrometer type 1.108 with 15 size bins from 0.3 to 20 μm was used, for the small particles > 10 nm a TSI 3010 particle counter. Temperature and dewpoint are measured with a fast chilled mirror (Meteolab, CH). All data are used to evaluate mixing layer height information.

Since more than a decade, several instruments using narrow field of view radiometers and applying time series, snapshots and scanning techniques have been developed to monitor down welling long wave radiations and by consequence cloud cover intensity. For regular monitoring of cloud cover, in atmospheric measurement networks the time series technique has already been used with ceilometric data and now with narrow field of view (NFOV) radiometers. In order to determine the best set of data for sampling frequency, zenith angle and also field of view, we built a numerical simulator calculating interactions between a measurement grid in the approximation of the parallel plan model and binarized cloud fields generated by the "Larges Eddies Simulation" method. We will present results obtained with various sets of radiometers with different geometries facing to cloud fields simulating a wide range of broken clouds conditions. As a conclusion, we provide recommendations for positioning and feature of NFOV radiometers and finally we will discuss potential improvements of these simulation techniques.

In order to characterize the solar UV radiation reaching the Earths surface it is monitored from space by means of (i) the clear-sky UV index at local solar noon, which is most relevant for operational UV forecasting, and (ii) the daily UV dose including cloud shielding effects, which is most relevant for long-term UV monitoring and assessments of health risks and biological UV effects. Optimal space- based surface UV monitoring combines information from platforms in different orbits. Space-based total ozone column products from polar orbiting platforms can be used adequately for UV monitoring because the diurnal variability in the total ozone column is limited. However, cloud cover and cloud optical thickness typically vary significantly on time scales of minutes to hours, especially over land in relation to convective activity. Because diurnal variations in cloud amount and cloud optical thickness impact dramatically on the daily-integrated UV radiation levels transmitted to the Earths surface, the time variations in (key) cloud parameters over the day need to be captured by observations. Sampling of the diurnal variations in clouds is most efficiently done from geostationary platforms. Here we demonstrate examples of calculations of the clear- sky UV index and the UV daily dose for erythema over Europe based on assimilated total ozone column data derived from observations by GOME aboard ERS-2 and its successor SCIAMACHY aboard ENVISAT, in combination with cloud information retrieved from MVIRI aboard Meteosat-7 and its successor SEVIRI aboard MSG (Meteosat-8). Some first validations with ground-based surface spectral UV data are presented.

Ultraviolet spectral irradiances are systematically recorded in Briancon (at an altitude of 1310 m), in the French Southern Alps. Up to now, aerosols optical depth (AOD) had never been routinely measured in Briancon, so it has appeared of great interest to take advantage of the many spectra recorded to learn more about aerosols over the spectral range: 320 nm - 448 nm. To retrieve AOD, one only has to remove the contribution of ozone and molecule from the total optical depth, obtained from the direct irradiance. The method has been implemented for every spectra acquired during clear sky days selected among the period from July 2004 to March 2005. Data recorded show that at a given wavelength, AOD is roughly constant during the day. Lowest values for AOD at 12:00 U. T. are found to be around 0.05 at 440 nm and 0.15 at 320 nm, and may increase threefold for some days. AOD range between 320 and 448 nm is larger in summer than in winter. This agrees with the way α, the Angstrom parameter, varies from one season to the other. Unfortunately, one can only make a restricted use of α, as its determination over the ultraviolet range is subject to high AOD uncertainties. The main source of AOD error rests in the 10% of uncertainty on direct irradiance measured. This gives rises to relatively high uncertainties on AOD, which increase all the more when aerosols load in the atmosphere is low. In Briancon, renowned for its air goodness, true AOD values are likely to be reached within 45% - 50% as the best in a majority of cases.

The Central UV Calibration Facility (CUCF) annually calibrates and characterizes 47 Ultraviolet Multi-Filter Rotating Shadow-band Radiometers (UV-MFRSR) for the USDA UV Monitoring and Research Program (UVMRP). The UV-MFRSR instrument has seven 2-nm wide channels with nominal centroids at 300, 305, 311, 317, 325, 332, and 368 nm. The first two channels 300 and 305 nm use silicon-carbide (SiC) photodiodes, and in the original design the remaining five channels used gallium-phosphide (GaP) photodiodes. Because of the high rate of failure in the channels with GaP photodiodes, channels 3 through 7 were replaced with silicon (Si) photodiodes starting in June 2000 by the manufacturer Yankee Environmental Systems, Inc. The newer design radiometers were tested for out-of-band rejection with two sources, in the laboratory using a 1000W FEL quartz tungsten halogen lamp and in the field using the sun. Out-of-band light measurements were completed in the field on all 47 radiometers and show there is no appreciable signal from out-of-band light contributing to the total solar horizontal irradiance in each of the seven wavelength bands. However, in the calibration procedure, using a 1000W FEL quartz- tungsten-halogen lamp there is significant out-of-band signal contributing to the measured signal. The out-of-band signal is measured at the time of the calibration and corrections are applied to the calibration factors of the radiometer in each channel. At the Table Mountain Test Facility, solar irradiance from a calibrated filter radiometer with and without the out-of-band correction factors are compared to filter weighted solar irradiance from the U111 reference spectroradiometer.

Aerosol amount (AOD) and optical properties single scattering albedo (SSA) and asymmetry parameter play a crucial role in determining the amount of UVB radiation reaching the Earth's surface as well as the energetic driver of tropospheric ozone pollution chemistry. Using a Baynesian optimal estimation technique pioneered by Rodgers approach that constructs a sensitivity type Jacobian resposne matrix from a forward model RT model, we obtain AOD and SSA at 7 UV wavelengths (300- 305-, 311-, 317-, 325-, 332-, and 368-nm). The basis of the technique rests on the direct to diffuse ratio, which is readily obtained by the UV Multi-filter Shadowband spectrometer (UV-MFRSR). We present a one month time series of aerosol optical properties from 3 sites close to 40° N, each with a different aerosol climate characteristics.

Accurate and automatic detection of clouds in satellite scenes is a key issue for a wide range of remote sensing applications. With no accurate cloud masking, undetected clouds are one of the most significant source of error in both sea and land cover biophysical parameter retrieval. Sensors with spectral channels beyond 1 um have demonstrated good capabilities to perform cloud masking. This spectral range can not be exploited by recently developed hyperspectral sensors that work in the spectral range between 400- 1000 nm. However, one can take advantage of their high number of channels and spectral resolution to increase the cloud detection accuracy, and to describe properly the detected clouds (cloud type, height, subpixel coverage, could shadows, etc.) In this paper, we present a methodology for cloud detection that could be used by sensors working in the VNIR range. First, physically-inspired features are extracted (TOA reflectance and their spectral derivatives, atmospheric oxygen and water vapour absorptions, etc). Second, growing maps are built from cloud-like pixels to select regions which potentially could contain clouds. Then, an unsupervised clustering algorithm is applied in these regions using all extracted features. The obtained clusters are labeled into geo-physical classes taking into account the spectral signature of the cluster centers. Finally, an spectral unmixing algorithm is applied to the segmented image in order to obtain an abundance map of the cloud content in the cloud pixels. As a direct consequence of the detection scheme, the proposed system is capable to yield probabilistic outputs on cloud detected pixels in the image, rather than flags. Performance of the proposed algorithm is tested on six CHRIS/Proba Mode 1 images, which presents a spatial resolution of 32 m, 62 spectral bands with 6-20 nm bandwidth, and multiangularity.

A method (atmospheric correction via simulated annealing (ACSA)) is proposed that enhances the atmospheric correction of hyperspectral images over dark surfaces. It is based on the minimization of a smoothness criterion to avoid the assumption of linear variations of the reflectance within gas absorption bands. We first show that this commonly used approach generally fails over dark surfaces when the signal to noise ratio strongly declines. In this case, important residual features highly correlated with the shape of gas absorption bands are observed in the estimated surface reflectance. We add a geometrical constraint to deal with this correlation. A simulated annealing approach is used to solve this constrained optimization problem. The parameters involved in the implementation of the algorithm (initial temperature, number of iterations, cooling schedule, and correlation threshold) are automatically determined using standard simulated annealing theory, reflectance databases, and sensor characteristics. Applied to a HyMap image with available ground truths, we verify that ACSA adequately recovers ground reflectance over clear land surfaces and that the added spectral shape constraint does not introduce any spurious feature in the spectrum. The analysis of an AVIRIS image clearly shows the ability of the method to perform enhanced water vapor estimations over dark surfaces. Over a lake (reflectance equal to 0.02, low signal to noise ratio equal to about 6), ACSA retrieves unbiased water vapor amounts (2.86 cm ± 0.36 cm) in agreement with in situ measurements (2.97 cm ± 0.30 cm). This corresponds to a reduction of the standard deviation by a factor 3 in comparison with standard unconstrained procedures (1.95 cm ± 1.08 cm). Similar results are obtained using a Hyperion image containing a very dark area of the land surface.

In this paper the problem of the light reflection from a turbid medium slab is considered. The method of the single scattering separation on a scattering leading to a radiative transfer veering concerning a surface normal, and on a scattering not leading to that is offered. The reflectance is represented as a series on the scattering multiplicities with a single change of the direction. For each multiplicity the precise linear integro-differential equation with homogeneous boundary conditions is obtained. The application of the discrete ordinates method brings to the linear matrix equations. The solution of these equations without usage of the small angle approximation in the matrix exponential curves form is found. The application range of the quasi-single scattering approximation is uniquely determined.

Based on the Matrix-Operator Method the radiative transfer code STORM (STOkes vector Radiative transfer Model) is introduced, which was developed in a joint project of DLR and Institut fuer Weltraumwissenschaften of the Freie Universitaet Berlin. STORM calculates the Stokes parameters (I, Q, U, V) in a plane parallel, multi layered atmosphere in the visible and near infrared spectral range. The scattering characteristics of aerosols are determined by Mie theory. The surface represents a Lambertian reflector or a wind ruffled water surface described by Cox-Munk model. The results of one calculation are the upward and downward directed Stokes parameters for one wavelength at a desired number of sun incident and viewing angles at varying altitudes in the principal plane and other azimuth angles. STORM is applied for an analysis in view of designing downward looking Earth observing optical remote sensing systems and values of the degree of polarization are presented as generic basis for remote sensing system design and data processing.

In order to achieve quantitative measurements of the Earth's surface radiance and reflectance, it is important to determine the aerosol optical thickness (AOT) to correct for the optical influence of atmospheric particles. An advanced method for aerosol detection and quantification is required, which is not strongly dependant on disturbing effects due to surface reflectance, gas absorption and Rayleigh scattering features. A short review of existing applicable methods to the APEX airborne imaging spectrometer (380nm to 2500nm), leads to the suggested aerosol retrieval method here in this paper. It will measure the distinct radiance change between two near-UV spectral bands (385nm & 412nm) due to aerosol induced scattering and absorption features. Atmospheric radiation transfer model calculations have been used to analyze the AOT retrieval capability and accuracy of APEX. The noise-equivalent differential AOT is presented along with the retrieval sensitivity to various input variables. It is shown, that the suggested method will be able to identify different aerosol model types and measure AOT and columnar size distribution. The proposed accurate AOT determination will lead to a unique opportunity of two-dimensional pixel-wise mapping of aerosol properties at a high spatial resolution. This will be helpful especially for regional climate studies, atmospheric pollution monitoring and for the improvement of aerosol dispersion models and the validation of aerosol algorithms on spaceborne sensors.

Knowledge of the size and chemical composition of aerosols is important to assess their role in several processes occurring in the atmosphere. The aerosol optical thickness is a byproduct of the atmospheric correction, but it is possible to research atmospheric aerosol by those byproducts. In this paper, we first calculated the aerosol optical thickness over other wavelengths using SeaWiFS-derived aerosol optical thickness at 865nm and atmospheric-correction parameters ε(λ,865). Then we classified the aerosol over the ocean into three classes: nuclei mode (r < 0.04μm), accumulation mode (0.04μm < r < 1.0μm) and coarse mode (r > 1.0μm), which are all described by the log-normal distribution. The derived relationship of aerosol optical thickness and number distribution at different wavelengths and Monte-Carlo method are used to obtained the total number of those three classes over the ocean and we analysis their distribution. The reasonable results show that the aerosol optical thickness by SeaWiFS is nice for atmospheric aerosol research.

For a better understanding of aerosols, simultaneous measurements of aerosols and suspended particulate matter(SPM) have been undertaken at Kinki University campus in Higashi-Osaka. The relationship between aerosol properties obtained from radiometry with a multi-spectral photometer as a NASA/AERONET station and SPM concentrations such as TSP, PM₁₀, PM_2.5, and OBC with SPM-613D (Kimoto Electric) is examined. It is found that there is a linear correlation between SPM concentrations and aerosol properties, which indicates that aerosol characteristics can be estimated from SPM data, and vice versa. It is also shown that the air quality of the Higashi-Osaka site is poor due to not only anthropogenic particles produced by local emissions, such as diesel vehicles and chemical industries, but also due to dust particles coming from continental desert areas by large scale climatic conditions. As a result, long term simultaneous monitoring of aerosols and SPM provides us with three types of particles according to the season for atmospheric aerosols at an industrial city of Higashi-Osaka.

The polarization data acquired by POLDER (Polarization and Directionality of Earth Reflectances) sensor on board the ADEOS (Advanced Earth Observing Satellite)-1 and 2 have shown that polarization information is useful to extract the aerosol properties over land as well as those over ocean. This work describes a procedure to retrieve aerosol characteristics such as AOT (Aerosol Optical Thickness), and its wavelength tendency (Angstrom exponent). These parameters indicate the basic information for amount and particle size of aerosols, respectively. It is found that aerosol loading in central Africa and Asia is always high from April to June, and increases from ADEOS-1 in 1997 to ADEOS-2 in 2003. The results retrieved from ADEOS/POLDER are validated with sun photometry by NASA/AERONET (Aerosol Robotic Network).

Aerosols direct and indirect effects on the Earth's climate are widely recognized but have yet to be adequately quantified. Difficulties arise due to the very high spatial and temporal variability of aerosols, which is a major cause of uncertainties in radiative forcing studies. The effective monitoring of the global aerosol distribution is only made possible by satellite monitoring and this is the reason why the interest in aerosol observations from satellite passive radiometers is steadily increasing. From the point of view of the study of land surfaces, the atmosphere with its constituents represents an obscurant whose effects should be as much as possible eliminated, being this process sometimes referred to as atmospheric correction. In absence of clouds and using spectral intervals where gas absorption can be avoided to a great extent, only the aerosol effect remains to be corrected. The monitoring of the aerosol particles present in the atmosphere is then crucial to succeed in doing an accurate atmospheric correction, otherwise the surface properties may be inadequately characterised. However, the atmospheric correction over land surfaces turns out to be a difficult task since surface reflection competes with the atmospheric component of the signal. On the other hand, a single mean pre-established aerosol characterisation would not be sufficient for this purpose due to very high spatial and temporal variability of aerosols and their unpredictability, especially what concerns particulary intense "events" such as biomass burning and forest fires, desert dust episodes and volcanic eruptions. In this context, an operational methodology has been developed at the University of Evora - Evora Geophysics Centre (CGE), in the framework of the Satellite Application Facility for Land Surface Analysis - Land SAF, to derive an Aerosol Product from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) data, flying on the Geostationary (GEO) satellite system Meteosat-8. The aerosol characterization obtained is used to calculate the fluxes and estimate the aerosol radiative forcing at the top of the atmosphere. The methodology along with the results of the aerosol properties and radiative forcing using SEVIRI images is presented. The aerosol optical thickness results are compared with ground-based measurements from the Aerosol Robotic NETwork (AERONET), to assess the accuracy of the methodology presented.

To gather information about the impact on the environment caused by airport operations, knowledge about the amount of gases such as CO or NO_X emitted by aircraft engines on the ground is important. In order to avoid influences on airport operations an analysis system for this application has to enable measurements on the hot jet engine exhaust gas from a distance. The infrared radiation emitted by the hot gas can be analysed by Fourier-transform infrared spectroscopy to determine the composition of the gas. To fulfil this task, a new version of the scanning infrared gas imaging system (SIGIS HR), using relatively high spectral resolution (0.2 cm^-1), has been developed. The period of time for measurements on the engine exhaust gas of an aircraft on the ground is short during normal airport operations. Hence the remote sensing system has to be aligned to the exhaust gas plume quickly. For this reason the system is equipped with a scanning mirror actuated by stepper motors in order to allow fast changes of the line of sight. An infrared camera combined with a DSP-system enables automatic alignment of the system to the hot exhaust gas and tracking of a moving engine via online analysis of the infrared image. Additionally fast scans with low spectral resolution of the area around the engine-outlet can be performed. On the basis of the low resolution data the optimal direction for the exhaust gas measurement can be found using several automatic evaluation- and positioning-algorithms. After the SIGIS HR-system has been positioned correctly it is operated in high- resolution-mode in order to quantify the target compounds.

Ecological monitoring and analysis of the planetary boundary layer (PBL) dynamics require determination of the mixing layer height (MLH) on a continuous basis. In a number of cases it is necessary to determine the MLH with sufficiently high resolution - both altitude and temporal. The backscatter lidar provides a convenient tool for such determination, using the aerosol as tracer and determining its vertical profile and its time-evolution, with the capability for continuous measurements. Although methods already exist, based on the altitude derivative of the backscatter lidar signal (altitude Gradient method) and its time-variance (Variance method), the application of these methods with high resolution is limited by the background noise presence. We report here a further development of backscatter lidar gradient and variance methods for MLH determination, allowing higher resolutions. In it, the MLH determination from the gradient and the variance of the lidar signal is supported by a convenient filter technique. Time scale of increased temporal resolution allows the investigation of the fine atmospheric dynamic structures like convective motion. A number of examples in MLH retrieval are presented. The examples are based on backscatter lidar measurements performed in the PBL above Neuchatel, Switzerland (47.00°N, 6.95°S, 485m asl). The examples show the applicability and the usefulness of the reported technique in measurements of the daily cycle of the MLH dynamics.

We report the upgraded version of two compact, airborne, automatic lidars, installed on the stratospheric research aircraft M55 "Geophysica". The lidars (named MAL1 and MAL2) are depolarisation backscatter instruments. They are installed on the aircraft for probing independently upwards and downwards with respect to the aircraft altitude, providing the possibility to detect the cloud presence simultaneously above and below the aircraft. The cloud parameters determined from the lidar signals are the followings: the altitude of the cloud base and cloud top, the backscatter ratio and the depolarisation ratio of the subvisible clouds. The measurements are at a single wavelength of 532 nm (the second harmonics of the Nd:YAG laser). The combination of the photon counting signal acquisition system, the pulse duty cycle and the output power of the micro-pulsed laser, leads to a high dynamic range of detection. Objectives of the lidar installation on this stratospheric aircraft are the measurements of high-altitude cirrus and polar stratospheric clouds, as well as aerosol layers in the middle and high troposphere. We present examples of measurements of backscatter and depolarisation ratio of sub-visible clouds performed with these lidars, during recent field campaigns: ESA ENVISAT Validation and EC projects EUPLEX (European Polar Stratospheric Clouds and Lee Wave Experiment). and TROCCINOX (Tropical Convection, Cirrus and Nitrogen Oxides Experiment).

The Advanced Technology Microwave Sounder (ATMS) meteorological flight instruments for use on board the NPOESS Preparatory Project (NPP) spacecraft and the National Polar-Orbiting Operational Environmental Satellite System (NPOESS), is a multi-channel microwave radiometer. The ATMS is a total power radiometer system that passively monitors the radiation from the Earth's surface and atmosphere in the microwave portion of the spectrum. It is a cross- track, line-scanned instrument designed to measure scene radiance's in twenty two discrete frequency channels. The paper presents instruments performance for first flight unit.

Factors affecting changes of spectral UV irradiance at the Sonnblick Observatory are studied. Spectral UV measurements at wavelengths from 290 nm to 400 nm performed during the period from 1994 to 2003 are used in this investigation. These measurements have been performed with a Brewer ozone single spectrophotometer and with a Bentham DM 150 spectroradiometer (double monochromator). The radiative transfer model DISORT (based on the Discrete Ordinate Method) was used in the simulations. Measurements of UV-radiation at Sonnblick at 305 nm under clear sky conditions show, that the snowline may influence the irradiance by mean by 24%. Cloudiness enhances the influence of the albedo since multiple reflections between surface and lower bond of the clouds become more probable. In presence of 8/8 cloud cover, UV irradiance at 305 nm is enhanced by a factor of 1.7 when the snowline is 800 m instead of 3000 m. In addition to the snowline, clouds situated below the Sonnblick are responsible for increased albedo and consequently increased radiation. Model calculations show that average albedo is increased by 0.28 ± 0.15 due to 4/8 cloud cover or more below the top of the mountain. The influence of ozone, albedo and clouds on UV variability is evaluated separately using 10-year climatology. It was found that the effect of total ozone on short- term variability of UV irradiance at 305 nm can be more than 200% and on average 56%. Clouds can cause variability of 150% or more and on average 35%.

Because gravity wave effects control middle atmosphere circulation patterns, and because those effects depend sensitively on the properties of the waves, reseachers have been trying for decades to ascertain the global properties of gravity waves to better constrain global circulation models. Space-based observations hold promise for providing the needed information, but the small scales of gravity waves have posed observational challenges. Traditional analyses of averaged temperature variance do not provide the needed information. We will present statistics from alternative analyses of Atmospheric Infrared Sounder (AIRS) images of gravity waves in the stratosphere. The high spatial resolution of the AIRS observations permit resolution of gravity waves with horizontal wavelengths as small as 50 km. We present the results of wavelet analyses of AIRS images at 667cm^-1 (in the CO₂ 15 μm band) that spatially resolve gravity wave amplitudes, horizontal wavelengths, and propagation directions. These analyses reveal both local maximum amplitudes as well as frequencies of wave occurrence, while in contrast these quantities are inseparably blended within traditional wave temperature variance or Fourier analysis methods. The AIRS observations are known to detect only long vertical wavelength waves, whose occurrences are in turn known to be highly dependent on the strength of background wind speeds. The AIRS data permit for the first time detailed studies of the relationships between the occurrence of these waves and their propagation directions relative to the background winds.